Mutant prevention concentrations of ciprofloxacin and enrofloxacin for Salmonella enterica

Objectives: To determine the mutant prevention concentrations (MPCs) of ciprofloxacin and enrofloxacin against four strains of Salmonella enterica serovar Enteritidis and four strains of S. Typhimurium including one fully susceptible, one multiply resistant (MAR), one GyrA mutant and one GyrA/MAR mutant. Further, to examine mutants arising after exposure to sub-MPC concentrations of the antibiotics for susceptibility to ciprofloxacin and enrofloxacin, and cyclohexane tolerance. Methods: MICs were determined using the agar dilution method of the BSAC. The MPC was recorded as the lowest concentration of antibiotic to inhibit growth from an inoculum of 10(10) cfu. Results: The MPCs and resulting MPC/MIC ratios of enrofloxacin were generally two- to four-fold higher than for ciprofloxacin. At 24 h for both antibiotics, MPCs were lowest for the fully susceptible strains (0.25-0.5 mg/L), similar for the MAR (1-4 mg/L) and GyrA (2-4 mg/L) mutants and highest for the GyrA/MAR mutants (1-8 mg/L). MPC/MIC ratios at 24 h were 2-16 for all strains except those for the MAR strains without mutation in gyrA where the ratios were 8-64. Conclusions: The ability to eradicate Salmonella in vivo depends on many factors such as antibiotic susceptibility of the strain, dose and route of administration. It is suggested that these MPC values will be useful when considering dosing strategies. In view of the high MPC/MIC ratio, MAR strains with wild-type gyrA, although susceptible to ciprofloxacin (MICs 0.06-0.13 mg/L), may give rise to treatment failures.

Screening for Bacillus isolates in the broiler gastrointestinal tract

Spores from a number of different Bacillus species are currently being used as human and animal probiotics, although their mechanisms of action remain poorly understood. Here we describe the isolation of 237 presumptive gut-associated Bacillus spp. isolates that were obtained by heat and ethanol treatment of fecal material from organically reared broilers followed by aerobic plating. Thirty-one representative isolates were characterized according to their morphological, physiological, and biochemical properties as well as partial 16S rRNA gene sequences and screening for the presence of plasmid DNA. The Bacillus species identified included B. subtilis, B. pumilus, B. licheniformis, B. clausii, B. megaterium, B. firmus, and species of the B. cereus group, whereas a number of our isolates could not be classified. Intrinsic properties of potential importance for survival in the gut that could be advantageous for spore-forming probiotics were further investigated for seven isolates belonging to five different species. All isolates sporulated efficiently in the laboratory, and the resulting spores were tolerant to simulated gastrointestinal tract conditions. They also exhibited antimicrobial activity against a broad spectrum of bacteria, including food spoilage and pathogenic organisms such as Bacillus spp., Clostridium perfringens, Staphylococcus aureus, and Listeria monocytogenes. Importantly, the isolates were susceptible to most of the antibiotics tested, arguing that they would not act as donors for resistance determinants if introduced in the form of probiotic preparations. Together, our results suggest that some of the sporeformers isolated in this study have the potential to persist in or transiently associate with the complex gut ecosystem.

Detection of mutations in Salmonella enterica gyrA, gyrB, parC and parE genes by denaturing high performance liquid chromatography (DHPLC) using standard HPLC instrumentation

Aims: Quinolone antibiotics are the agents of choice for treating systemic Salmonella infections. Resistance to quinolones is usually mediated by mutations in the DNA gyrase gene gyrA. Here we report the evaluation of standard HPLC equipment for the detection of mutations (single nucleotide polymorphisms; SNPs) in gyrA, gyrB, parC and parE by denaturing high performance liquid chromatography (DHPLC). Methods: A panel of Salmonella strains was assembled which comprised those with known different mutations in gyrA (n = 8) and fluoroquinolone-susceptible and -resistant strains (n = 50) that had not been tested for mutations in gyrA. Additionally, antibiotic-susceptible strains of serotypes other than Salmonella enterica serovar Typhimurium strains were examined for serotype-specific mutations in gyrB (n = 4), parC (n = 6) and parE (n = 1). Wild-type (WT) control DNA was prepared from Salmonella Typhimurium NCTC 74. The DNA of respective strains was amplified by PCR using Optimase (R) proofreading DNA polymerase. Duplex DNA samples were analysed using an Agilent A1100 HPLC system with a Varian Helix (TM) DNA column. Sequencing was used to validate mutations detected by DHPLC in the strains with unknown mutations. Results: Using this HPLC system, mutations in gyrA, gyrB, parC and parE were readily detected by comparison with control chromatograms. Sequencing confirmed the gyrA predicted mutations as detected by DHPLC in the unknown strains and also confirmed serotype-associated sequence changes in non-Typhimurium serotypes. Conclusions: The results demonstrated that a non-specialist standard HPLC machine fitted with a generally available column can be used to detect SNPs in gyrA, gyrB, parC and parE genes by DHPLC. Wider applications should be possible.

Fluoroquinolone treatment of experimental Salmonella enterica serovar Typhimurium DT104 infections in chickens selects for both gyrA mutations and changes in efflux pump gene expression

Objectives: To determine the efficacy of enrofloxacin (Baytril) in chickens in eradicating three different resistance phenotypes of Salmonella enterica and to examine the resistance mechanisms of resulting mutants. Methods: In two separate replicate experiments (I and 11), three strains of Salmonella enterica serovar Typhimurium DT104 [strain A, fully antibiotic-sensitive strain; strain B, isogenic multiple antibiotic-resistant (MAR) derivative of A; strain C, veterinary penta-resistant phenotype strain containing GyrA Phe-83], were inoculated into day-old chicks at similar to 10(3) Cfu/bird. At day 10, groups of chicks (n =10) were given either enrofloxacin at 50 ppm in their drinking water for 5 days or water alone (control). Caecal contents were monitored for presence of Salmonella and colonies were replica plated to media containing antibiotics or overlaid with cyclohexane to determine the proportion of isolates with reduced susceptibility. The MICs of antibiotics and cyclohexane tolerance were determined for selected isolates from the chicks. Mutations in topoisomerase genes were examined by DHPLC and expression of marA, soxS, acrB, acrD and acrF by RT-PCR. Results: In experiment 1, but not 11, enrofloxacin significantly reduced the numbers of strain A compared with the untreated control group. In experiment 11, but not 1, enrofloxacin significantly reduced the numbers of strain B. Shedding of strain C was unaffected by enrofloxacin treatment. Birds infected with strains A and B gave rise to isolates with decreased fluoroquinolone susceptibility. Isolates derived from strain A or B requiring > 128 mg/L nalidixic acid for inhibition contained GyrA Asn-82 or Phe-83. Isolates inhibited by 16 mg/L nalidixic acid were also less susceptible to antibiotics of other chemical classes and became cyclohexane-tolerant (e.g. MAR). Conclusions: These studies demonstrate that recommended enrofloxacin treatment of chicks rapidly selects for strains with reduced fluoroquinolone susceptibility from fully sensitive and MAR strains. It can also select for MAR isolates.

The AcrAB-TolC efflux system of Salmonella enterica serovar Typhimurium plays a role in pathogenesis

The ability of an isogenic set of mutants of Salmonella enterica serovar Typhimurium L354 (SL1344) with defined deletions in genes encoding components of tripartite efflux pumps, including acrB, acrD, acrF and tolC, to colonize chickens was determined in competition with L354. In addition, the ability of L354 and each mutant to adhere to, and invade, human embryonic intestine cells and mouse monocyte macrophages was determined in vitro. The tolC and acrB knockout mutants were hyper-susceptible to a range of antibiotics, dyes and detergents; the tolC mutant was also more susceptible to acid pH and bile and grew more slowly than L354. Complementation of either gene ablated the phenotype. The tolC mutant poorly adhered to both cell types in vitro and was unable to invade macrophages. The acrB mutant adhered, but did not invade macrophages. In vivo, both the acrB mutant and the tolC mutant colonized poorly and did not persist in the avian gut, whereas the acrD and acrF mutant colonized and persisted as well as L354. These data indicate that the AcrAB-TolC system is important for the colonization of chickens by S. Typhimurium and that this system has a role in mediating adherence and uptake into target host cells.

Effect of fluoroquinolone exposure on the proteome of Salmonella enterica serovar Typhimurium

Objectives: The physiological response of Salmonella enterica serovar Typhimurium to fluoroquinolone antibiotics was investigated using proteomic methods. Methods: Proteomes were prepared from strain SL1344 following treatment of broth cultures with ciprofloxacin (0.03 and 0.008 mg/L; 2x and 0.5x MIC) and enrofloxacin (0.03 mg/L) and from a multiple antibiotic resistant (MAR) mutant. Protein expression was determined by two-dimensional HPLC-MSn and also after exposure to ciprofloxacin by two-dimensional gel electrophoresis (2D-GE). Results: The number of proteins (mean +/- SD) detected by 2D-GE derived from control cultures of the wild-type strain was significantly (P < 0.05) reduced from 296 +/- 77 to 153 +/- 36 following treatment with ciprofloxacin (0.03 mg/L). Raised expression (P < 0.05) of 17 proteins was also detected, and increases of up to 8-fold (P < 0.0001) were observed for subunits of F1F0-ATP synthase, TolC and Imp. Analysis by two-dimensional HPLC-MSn provided higher proteome coverage with 787 +/- 50 proteins detected, which was reduced (P < 0.005) to 560 +/- 14 by ciprofloxacin (0.03 mg/L). Increased expression of 43 proteins was observed which included those detected by 2D-GE and additionally the efflux pump protein AcrB. The basal expression of the AcrAB/TolC efflux pump was elevated in the MAR mutant compared with the untreated wild-type and augmented following treatment with ciprofloxacin (0.03 mg/L). F1F0-ATP synthase and Imp were only elevated in the mutant when treated with ciprofloxacin. Conclusions: These studies suggest that increased expression of AcrAB/TolC was associated with resistance while other increases, such as in F1F0-ATP synthase and Imp, were a response to fluoroquinolone.

Prolonged treatment of Salmonella enterica serovar Typhimurium with commercial disinfectants selects for multiple antibiotic resistance, increased efflux and reduced invasiveness

Objectives: To study how disinfectants affect antimicrobial susceptibility and phenotype of Salmonella enterica serovar Typhimurium SL1344. Methods: Wild-type strain SL1344 and its isogenic gyrA mutant were passaged daily for 7 days in subinhibitory concentrations, and separately for 16 days in gradually increasing concentrations of a quaternary ammonium disinfectant containing formaldehyde and glutaraldehyde (QACFG), an oxidizing compound blend (OXC), a phenolic tar acids-based disinfectant (TOP) and triclosan. The MICs of antimicrobials and antibiotics for populations and representative isolates and the proportion of cells resistant to the MICs for the wild-type were determined. Expression of acrB gene, growth at 37 degrees C and invasiveness of populations in Caco-2 intestinal epithelial cells were assessed. Results: QACFG and triclosan showed the highest selectivity for variants with reduced susceptibility to chloramphenicol, tetracycline, ampicillin, acriflavine and triclosan. Populations treated with the above biocides had reduced invasiveness in Caco-2 cells, and altered growth kinetics. Resistance to disinfectants was observed only after exposure to gradually increasing concentrations of triclosan, accompanied with a 2000-fold increase in its MIC. Growth in OXC and TOP did not affect the MICs of antibiotics, but resulted in the appearance of a proportion of cells resistant to the MIC of acriflavine and triclosan for the wild-type. Randomly selected stable variants from all populations, except the one treated with TOP, over-expressed acrB. Conclusions: In vitro exposure to QACFG and triclosan selects for Salmonella Typhimurium cells with reduced susceptibility to several antibiotics. This is associated with overexpression of AcrAB efflux pump, but accompanied with reduced invasiveness.

Developing consensus on hospital prescribing indicators of potential harms amenable to decision support

Aim: To develop a list of prescribing indicators specific for the hospital setting that would facilitate the prospective collection of high severity and/or high frequency prescribing errors, which are also amenable to electronic clinical decision support (CDS). Method: A three-stage consensus technique (electronic Delphi) was carried out with 20 expert pharmacists and physicians across England. Participants were asked to score prescribing errors using a 5-point Likert scale for their likelihood of occurrence and the severity of the most likely outcome. These were combined to produce risk scores, from which median scores were calculated for each indicator across the participants in the study. The degree of consensus between the participants was defined as the proportion that gave a risk score in the same category as the median. Indicators were included if a consensus of 80% or more was achieved. Results: A total of 80 prescribing errors were identified by consensus as being high or extreme risk. The most common drug classes named within the indicators were antibiotics (n=13), antidepressants (n=8), nonsteroidal anti-inflammatory drugs (n=6), and opioid analgesics (n=6).The most frequent error type identified as high or extreme risk were those classified as clinical contraindications (n=29/80). Conclusion: 80 high risk prescribing errors in the hospital setting have been identified by an expert panel. These indicators can serve as the basis for a standardised, validated tool for the collection of data in both paperbased and electronic prescribing processes, as well as to assess the impact of electronic decision support implementation or development.

Expression of cyclooxygenase-2 in intestine of pigs of different ages and hygiene status

Prostaglandins (PG) are bioactive lipids derived from the metabolism of membrane polyunsaturated fatty acids (PUFA), and play important roles in a number of biological processes including cell division, immune responses and wound healing. Cyclooxygenase (COX) is the key enzyme in PG synthesis from arachidonic acid. The hypothesis of the present study was that expression of COX-2 in porcine intestine was dependent on the microbial load and the age of piglets. Piglets were obtained from sows raised either on outdoor free-range farms or on indoor commercial farms, and littermates were divided into three treatments: One group of piglets suckled the sow, a second group was put into an isolator and fed a milk formula, and a third group was put into the isolator fed milk formula and injected with broad spectrum antibiotics. Samples were collected from the 75% level of the small intestine at day 5, 28 and 56 of age. Tissue section from four piglets from each of these six treatment groups was analysed by immunofluorescence for COX-2 and type-IV collagen (basement membrane, defining lamina propria (LP)). Image analysis was used to determine the number of positive pixels expressing LP and epithelial COX-2. COX-2 expressing cells were observed in LP and epithelium in all porcine intestinal samples. When analysing images obtained on day 28, injection of antibiotics seemed to reduce the COX-2 expression in intestinal samples of piglets when compared to other treatments (P=0.053). No significant effect of farm, treatments or age of piglets was observed on COX-2 expressing data when analysing all data of images obtained at day 28 and 56. By double-labelling experiments, COX-2 was found not to be expressed on cell co-expressing CD45, CD16, CD163 or CD2, thus indicating that mucosal leukocytes, including dendritic cells, macrophages and NK cells did not express COX-2. Future research should investigate the role of COX-2 expression in the digestive tract in relation to pig health.

Postnatal development of the mucosal immune system and consequences on health in adulthood

The intestinal microbiota is a dynamic multifaceted ecosystem which has evolved a complex and mutually beneficial relationship with the mammalian host. The contribution to host fitness is evident, but in recent years it has become apparent that these commensal microorganisms may exert far more influence over health and disease than previously thought. The gut microbiota are implicated in many aspects of biological function, such as metabolism, angiogenesis and immune development: disruption, especially during the neonatal period, which may impose life-long penalty. Elimination of the microbiota appears difficult, but manipulation of the ratios and dominance of composite populations can be achieved by alterations in diet, rearing environment, antibiotics and/or probiotics. Components of the intestinal microbiota are frequently documented to affect normal function of the mucosal immune system in experimental animals and in domesticated, agricultural species. However, it is not always clear that the effects described are sufficiently well understood to provide a sound basis for commercial intervention. Some microbial interventions may be beneficial to the host under particular circumstances, while detrimental during others. It is essential that we further our understanding of the complex and intricate host-commensal relationship to avoid causing more long-term damage than advantage

Anionic metabolic profiling of urine from antibiotic-treated rats by capillary electrophoresis–mass spectrometry

A recently developed capillary electrophoresis (CE)-negative-ionisation mass spectrometry (MS) method was used to profile anionic metabolites in a microbial-host co-metabolism study. Urine samples from rats receiving antibiotics (penicillin G and streptomycin sulfate) for 0, 4, or 8 days were analysed. A quality control sample was measured repeatedly to monitor the performance of the applied CE-MS method. After peak alignment, relative standard deviations (RSDs) for migration time of five representative compounds were below 0.4 %, whereas RSDs for peak area were 7.9–13.5 %. Using univariate and principal component analysis of obtained urinary metabolic profiles, groups of rats receiving different antibiotic treatment could be distinguished based on 17 discriminatory compounds, of which 15 were downregulated and 2 were upregulated upon treatment. Eleven compounds remained down- or upregulated after discontinuation of the antibiotics administration, whereas a recovery effect was observed for others. Based on accurate mass, nine compounds were putatively identified; these included the microbial-mammalian co-metabolites hippuric acid and indoxyl sulfate. Some discriminatory compounds were also observed by other analytical techniques, but CE-MS uniquely revealed ten metabolites modulated by antibiotic exposure, including aconitic acid and an oxocholic acid. This clearly demonstrates the added value of CE-MS for nontargeted profiling of small anionic metabolites in biological samples.

Human microbiota in health and disease

Each human body plays host to a microbial population which is both numerically vast (at around 1014 microbial cells) and phenomenally diverse (over 1,000 species). The majority of the microbial species in the gut have not been cultured but the application of culture-independent approaches for high throughput diversity and functionality analysis has allowed characterisation of the diverse microbial phylotypes present in health and disease. Studies in monozygotic twins, showing that these retain highly similar microbiota decades after birth and initial colonisation, are strongly indicative that diversity of the microbiome is host-specific and affected by the genotype. Microbial diversity in the human body is reflected in both richness and evenness. Diversity increases steeply from birth reaching its highest point in early adulthood, before declining in older age. However, in healthy subjects there appears to be a core of microbial phylotypes which remains relatively stable over time. Studies of individuals from diverse geopraphies suggest that clusters of intestinal bacterial groups tend to occur together, constituting ‘enterotypes’. So variation in intestinal microbiota is stratified rather than continuous and there may be a limited number of host/microbial states which respond differently to environmental influences. Exploration of enterotypes and functional groups may provide biomarkers for disease and insights into the potential for new treatments based on manipulation of the microbiome. In health, the microbiota interact with host defences and exist in harmonious homeostasis which can then be disturbed by invading organisms or when ‘carpet bombing’ by antibiotics occurs. In a portion of individuals with infections, the disease will resolve itself without the need for antibiotics and microbial homeostasis with the host’s defences is restored. The administration of probiotics (live microorganisms which when administered in adequate amounts confer a health benefit on the host) represents an artificial way to enhance or stimulate these natural processes. The study of innate mechanisms of antimicrobial defence on the skin, including the production of numerous antimicrobial peptides (AMPs), has shown an important role for skin commensal organisms. These organisms may produce AMPs, and also amplify the innate immune responses to pathogens by activating signalling pathways and processing host produced AMPs. Research continues into how to enhance and manipulate the role of commensal organisms on the skin. The challenges of skin infection (including diseases caused by multiply resistant organisms) and infestations remain considerable. The potential to re-colonise the skin to replace or reduce pathogens, and exploring the relationship between microbiota elsewhere and skin diseases are among a growing list of research targets. Lactobacillus species are among the best known ‘beneficial’ bacterial members of the human microbiota. Of the approximately 120 species known, about 15 are known to occur in the human vagina. These organisms have multiple properties, including the production of lactic acid, hydrogen peroxide and bacteriocins, which render the vagina inhospitable to potential pathogens. Depletion of the of the normal Lactobacillus population and overgrowth of vaginal anaerobes, accompanied by the loss of normal vaginal acidity can lead to bacterial vaginosis – the commonest cause of abnormal vaginal discharge in women. Some vaginal anaerobes are associated with the formation of vaginal biofilms which serve to act as a reservoir of organisms which persists after standard antibiotic therapy of bacterial vaginosis and may help to account for the characteristically high relapse rate in the condition. Administration of Lactobacillus species both vaginally and orally have shown beneficial effects in the treatment of bacterial vaginosis and such treatments have an excellent overall safety record. Candida albicans is a frequent coloniser of human skin and mucosal membranes, and is a normal part of the microbiota in the mouth, gut and vagina. Nevertheless Candida albicans is the most common fungal pathogen worldwide and is a leading cause of serious and often fatal nosocomial infections. What turns this organism from a commensal to a pathogen is a combination of increasing virulence in the organism and predisposing host factors that compromise immunity. There has been considerable research into the use of probiotic Lactobacillus spp. in vaginal candidiasis. Studies in reconstituted human epithelium and monolayer cell cultures have shown that L. rhamnosus GG can protect mucosa from damage caused by Candida albicans, and enhance the immune responses of mucosal surfaces. Such findings offer the promise that the use of such probiotic bacteria could provide new options for antifungal therapy. Studies of changes of the human intestinal microbiota in health and disease are complicated by its size and diversity. The Alimentary Pharmabiotic Centre in Cork (Republic of Ireland) has the mission to ‘mine microbes for mankind’ and its work illustrates the potential benefits of understanding the gut microbiota. Work undertaken at the centre includes: mapping changes in the microbiota with age; studies of the interaction between the microbiota and the gut; potential interactions between the gut microbiota and the central nervous system; the potential for probiotics to act as anti-infectives including through the production of bacteriocins; and the characterisation of interactions between gut microbiota and bile acids which have important roles as signalling molecules and in immunity. The important disease entity where the role of the gut microbiota appears to be central is the Irritable Bowel Syndrome (IBS). IBS patients show evidence of immune activation, impaired gut barrier function and abnormal gut microbiota. Studies with probiotics have shown that these organisms can exert anti-inflammatory effects in inflammatory bowel disease and may strengthen the gut barrier in IBS of the diarrhoea-predominant type. Formal randomised trials of probiotics in IBS show mixed results with limited benefit for some but not all. Studies confirm that administered probiotics can survive and temporarily colonise the gut. They can also stimulate the numbers of other lactic acid bacilli in the gut, and reduce the numbers of pathogens. However consuming live organisms is not the only way to influence gut microbiota. Dietary prebiotics are selectively fermented ingredients that can change the composition and/or activity of the gastrointestinal microbiota in beneficial ways. Dietary components that reach the colon, and are available to influence the microbiota include poorly digestible carbohydrates, such as non-starch polysaccharides, resistant starch, non-digestible oligosaccharides (NDOs) and polyphenols. Mixtures of probiotic and prebiotic ingredients that can selectively stimulate growth or activity of health promoting bacteria have been termed ‘synbiotics’. All of these approaches can influence gut microbial ecology, mainly to increase bifidobacteria and lactobacilli, but metagenomic approaches may reveal wider effects. Characterising how these changes produce physiological benefits may enable broader use of these tactics in health and disease in the future. The current status of probiotic products commercially available worldwide is less than ideal. Prevalent problems include misidentification of ingredient organisms and poor viability of probiotic microorganisms leading to inadequate shelf life. On occasions these problems mean that some commercially available products cannot be considered to meet the definition of a probiotic product. Given the potential benefits of manipulating the human microbiota for beneficial effects, there is a clear need for improved regulation of probiotics. The potential importance of the human microbiota cannot be overstated. ‘We feed our microbes, they talk to us and we benefit. We just have to understand and then exploit this.’ (Willem de Vos).

Messages about antibiotic resistance in different newspaper genres

Poorer people are more likely to use antibiotics; inappropriate antibiotic use causes resistance, and health campaigns attempt to change behaviour through education. However, fuelled by the media, the public think antibiotic resistance is outside their control. Differences in the attribution of blame for antibiotic resistance in two genres of UK newspapers, targeting distinct socioeconomic groups, were examined using a mixed methods approach. Firstly, depiction of blame was categorised as either external to the lay public (outside their control) or internal (lay person accountable) and subjected to a chi-square test. Secondly, using critical discourse analysis, we examined the portrayal of the main agents through newspaper language. Data from 597 articles (307 broadsheets) analysed revealed a significant association between newspaper genre and attribution of blame for antibiotic resistance. While both newspaper types blamed antibiotic resistance predominantly on factors external to the lay public, broadsheets were more likely to acknowledge internal factors than tabloids. Tabloids provided a more skewed representation, exposing readers to inaccurate explanations about antibiotic resistance. They highlighted ineptitude in health professionals, victimising patients and blaming others, while broadsheets used less emotive language. Pharmacists should take special care to communicate the importance of appropriate antibiotic use against this backdrop of distortion.

A pig’s microbiota – a result of many factors

Piglets can be reared under a variety of conditions ranging from outdoor, organic farms to high intensity, indoor facilities which use prophylactic antibiotics and everything in between. Do these different early-life influences matter when it comes to longer-term health and productivity?

Selection of potential probiotic lactic acid bacteria from fermented olives by in vitro tests

The present study aims to evaluate the probiotic potential of lactic acid bacteria (LAB) isolated from naturally fermented olives and select candidates to be used as probiotic starters for the improvement of the traditional fermentation process and the production of newly added value functional foods. Seventy one (71) lactic acid bacterial strains (17 Leuconostoc mesenteroides, 1 Ln. pseudomesenteroides, 13 Lactobacillus plantarum, 37 Lb. pentosus, 1 Lb. paraplantarum, and 2 Lb. paracasei subsp. paracasei) isolated from table olives were screened for their probiotic potential. Lb. rhamnosus GG and Lb. casei Shirota were used as reference strains. The in vitro tests included survival in simulated gastrointestinal tract conditions, antimicrobial activity (against Listeria monocytogenes, Salmonella Enteritidis, Escherichia coli O157:H7), Caco-2 surface adhesion, resistance to 9 antibiotics and haemolytic activity. Three (3) Lb. pentosus, 4 Lb. plantarum and 2 Lb. paracasei subsp. paracasei strains demonstrated the highest final population (>8 log cfu/ml) after 3 h of exposure at low pH. The majority of the tested strains were resistant to bile salts even after 4 h of exposure, while 5 Lb. plantarum and 7 Lb. pentosus strains exhibited partial bile salt hydrolase activity. None of the strains inhibited the growth of the pathogens tested. Variable efficiency to adhere to Caco-2 cells was observed. This was the same regarding strains' susceptibility towards different antibiotics. None of the strains exhibited β-haemolytic activity. As a whole, 4 strains of Lb. pentosus, 3 strains of Lb. plantarum and 2 strains of Lb. paracasei subsp. paracasei were found to possess desirable in vitro probiotic properties similar to or even better than the reference probiotic strains Lb. casei Shirota and Lb. rhamnosus GG. These strains are good candidates for further investigation both with in vivo studies to elucidate their potential health benefits and in olive fermentation processes to assess their technological performance as novel probiotic starters.